The Lord says to the church that if only two or three gather together and pray in agreement according to His commands, they will receive what they ask from God’s sovereign power.  “Wheresoever two or three are gathered in My name, I am with them,” He says. That is, He is with the simple and peaceable, with those who fear God and keep His commandments. Although only two or three, God will treat them in the same way that He treated the three youths in the fiery furnace. Because they lived for God unconditionally and in unity, He gave them life with breath of dew in the midst of the surrounding flames. In the same way, He was present with the two apostles shut up in prison, because they were devoted and of one mind.  Having loosened the bolts of the dungeon, He placed them in the marketplace to declare the Word they had faithfully preached.  Therefore, when he sys in His commandments, “Where two or three are gathered together in my name, I am with them.”  He rebukes the faithless for their disagreements and entrusts peace to the faithful by His word.  He shows that He is with two or three who pray with one mind, rather that with a large number who differ.  More can be obtained by the unified prayer of a few than by the disunited supplication of many.

- Cyprian

Taken from Day by Day with the Early Church Fathers, page 155.